1. Field of the Invention
The invention relates to a control device for an internal combustion engine and, more particularly, to a control device that switches control algorithms of an actuator constituting the internal combustion engine between two control algorithms.
2. Description of Related Art
Various actuators such as a throttle, an EGR valve, and a variable nozzle are disposed in an internal combustion engine, and an operation of the internal combustion engine is controlled based on operations of these actuators. These actuators have operation amounts that continuously vary or vary in stages. Command values that determine the operation amounts are calculated by a control device. The calculation of the command values is performed in accordance with control algorithms of the actuators. In a case where the actuator is controlled by a feedforward control (hereinafter, referred to as an FF control) and a feedback control (hereinafter, referred to as an FB control), for example, the command value is calculated as the sum of a feedforward term (hereinafter, referred to as an FF term) and a feedback term (hereinafter, referred to as an FB term). Specifically, the FB term is any one of a P term, an I term, and a D term or a combination thereof.
In some cases, a plurality of the control algorithms are selectively applied to one of the actuators. Switching from one of the control algorithms to another control algorithm results in switching of command value calculation methods, and thus the command value might go through a sudden change immediately after the switching. The sudden change in the command value for the actuator gives rise to a fluctuation in a control amount controlled by the operation of the actuator. The change in the command value may be suppressed by filter processing and averaging processing when only the suppression of the sudden change in the command value is intended. In a case where such processing is performed on the command value, however, controllability regarding the control amount itself is reduced. Accordingly, the suppression of the sudden change in the command value that occurs during the switching of the control algorithms without a reduction in the controllability has been pursued for a while.
Japanese Patent Application Publication No. 2007-218144 (JP 2007-218144 A) and Japanese Patent Application Publication No. 2006-275172 (JP 2006-275172 A) disclose techniques for suppressing the sudden change in the command value that occurs during the switching of the control algorithms. Hereinafter, an overview and problems thereof will be described.
JP 2007-218144 A discloses a control device that switches a control algorithm of a high-pressure pump of a fuel injection system between an FF-FB combination control in which an FF control and an FB control are used in combination and an FB single control in which only the FB control is executed. This control device is configured to set an FF term for the FF control prior to switching as an initial value of an I term for the FB control after switching during the switching from the FF-FB combination control to the FB single control. In addition, this control device is configured to set the I term for the FB control as an initial value of the FF term for the FF control after switching during the switching from the FB single control to the FF-FB combination control.
JP 2006-275172 A discloses a control device that switches a control algorithm of a solenoid valve for hydraulic control of a belt-type continuously variable transmission between a first control in which both an FF control and an FB control are executed and a second control in which only the FB control is executed. This control device is configured to add an FF term for the FF control prior to switching and an I term for the FB control at the point in time of switching to each other and set the result as an initial value of the I term for the FB control after switching during the switching from the first control to the second control. In addition, this control device is configured to subtract the FF term for the FF control at the point in time of switching from the I term for the FB control prior to switching and set the result as an initial value of the I term for the FB control after switching during the switching from the second control to the first control.